Passive projection screen for presenting projected images in 3D

ABSTRACT

A directive projection screen is configured to present images projected from a remote projector in three dimensions (3D) to a viewer. The screen includes a plurality of passive optical elements arranged on a structural substrate. The optical elements are configured to receive incident light projected from the projector and reflect the light such that first portions of the image are directed in a first direction to be viewed by a first eye of the viewer and second portions of the image are directed in a second direction to be viewed by a second eye of the viewer.

This Application claims priority to U.S. patent application Ser. No.13/528,742, filed Jun. 20, 2012, and entitled “Passive Projection Screenfor Presenting Projected Images in 3D”, which is incorporated herein byreference.

BACKGROUND

Passive display screens are used to present images that are projected bya projector. Home entertainment systems often use projection systems toproject images onto a passive screen to provide a big screen, highquality viewing experience. Unfortunately, passive display screenssuffer significant loss of image contrast due to light fromnon-projector sources, such as room lights, daylight from windows, andso forth. As a result, quality of the image presented on existingpassive display screens is poor. Further, traditional passive displayscreens typically reflect the projected image as a two-dimensional (2D)image. For users to experience three-dimensional (3D) images, such as ata theater, users are often required to wear special 3D glasses toconvert the 2D image into a 3D experience.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference numbers in different figures indicates similaror identical components or features.

FIG. 1 shows an illustrative scene containing a projector, severalnon-projector light sources, and a passive projection screen that may beconfigured to present images in either 2D or 3D.

FIG. 2 illustrates an acceptance cone and a viewing cone as well as thereflection and rejection of light impinging on the directive projectionscreen from different angles.

FIG. 3 illustrates an enlarged portion of a directive projection screencomprising optical waveguides.

FIG. 4 illustrates an enlarged portion of a directive projection screencomprising an array of tapered optical guides.

FIG. 5 illustrates an enlarged portion of a directive projection screencomprising an array of convex lenses having front surfaces and backsurfaces with back reflectors.

FIG. 6 illustrates an enlarged portion of a directive projection screencomprising a convex lens array with an optical absorber having aperturesand back reflectors.

FIG. 7 illustrates an alternative arrangement of elements in the passivedirective projection screen to enable a 3D experience for a user.

FIG. 8 illustrates an enlarged portion of a directive projection screenhaving elements comprised of wells and reflectors that direct differentparts of the image toward the left eye or right eye of the human viewer.

FIG. 9 illustrates an enlarged portion of a directive projection screenin which two different polarized filters are overlaid on the wells orcavities to selectively allow a viewer to see first optical elementswith one polarity with a left eye and second optical elements withanother polarity with a right eye.

FIG. 10 illustrates a directive projection screen that provides a 3Deffect in an image projected thereon by two projectors.

FIG. 11 illustrates a directive projection screen that utilizes aparallax barrier and alternating polarization patterns to create a 3Deffect in an image projected thereon.

FIG. 12 shows one example alternating polarization pattern used in thescreen of FIG. 11.

FIG. 13 illustrates a portable passive projection screen having a firstside with a surface that facilitates viewing of projected images in 2Dand a second side with a surface that facilitates viewing of projectedimages in 3D.

DETAILED DESCRIPTION

Projection systems are used in a variety of environments including movietheaters, conference rooms, classrooms, homes, and so forth. Theseprojection systems include a projector configured to emit light towardsa projection surface or screen. The projection surface in turn isconfigured to accept and scatter the light such that an image ispresented to viewers. The projection surface may be fixed, such as onethat mounts to a wall or a stand, or portable, such as a handheldprojection screen.

Existing projection surfaces suffer degradation of the presented imageresulting from non-projector light sources such as windows lettingdaylight in, room lights, and so forth. This degradation takes the formof loss of image contrast, which may be visualized as a “washing out” ofthe image. Further, traditional projection surfaces simply reflectprojected images in a flat two-dimensional (2D) image.

Disclosed herein are directive projection screens that provide higherquality images as compared to existing passive projection screens. Thesedirective projection screens are configured such that light from aprojector within a pre-determined acceptance cone of the projectionscreen is scattered and reflected for presentation, while light outsideof the acceptance cone is not reflected to the viewer. The screensdescribed herein provide improved gain of the projected image. As aresult, the directive projection screens described herein result inimproved contrast and image presentation to viewers.

Further, the directive projection screen can be configured with featuresthat enable the image to appear to the user in three-dimensions (3D)without aid of special 3D glasses. By orienting the features in apredetermined pattern, the passive screen reflects a portion of theprojected image in a direction suitable for left eye viewing and anotherportion of the projected image in another direction suitable for righteye viewing. The two directions define a parallax that yields a 3Dexperience for the viewer.

To enable a 3D appearance with this passive screen, the projectorprojects an image with pixel sizes smaller than the feature size. Theprojection system tracks the image on the screen to determine whichpixels of the projected image appear in left features and thus would bevisible by the left eye and which pixels appear in the right featuresand thus would be visible by the right eye. This map of left and righteye pixels is used to display the left and right image components forthe viewer to see a 3D image. In other implementations, polarizationelements may be used to eliminate or reduce the need for the projectionsystem to track the image.

The projection system with a passive directive screen may be implementedin many ways. One illustrative implementation is described below inwhich the projection system is implemented as part of an augmentedrelative environment within a room. However, the system may beimplemented in many other contexts and situations in which images areprojected onto screens for view consumption.

Illustrative Environment

FIG. 1 shows an illustrative environment 100 in which a projectionsystem with a passive directive projection screen may be used. Theenvironment 100 includes a projector 102 provided within a room, such asa room of a home, a conference room, and the like. In this illustration,the projector 102 is implemented as part of an augmented realityfunctional node, which includes one or more projectors and one or morecameras to capture projected images or patterns. The projector 102 isshown mounted to the ceiling of the room, although it may be placed inother locations. The projector 102 may be implemented with any number oftechnologies capable of generating an image and projecting that imageonto a surface. Suitable technologies include a digital micromirrordevice (DMD), liquid crystal on silicon display (LCOS), liquid crystaldisplay, 3LCD, laser projector, and so forth. In some implementations, aplurality of projectors 102 may be used.

The projector 102 has a projector field of view which describes aparticular solid angle. Along the center of this solid angle may bevisualized a line of projection 104 which extends to a center of animage 106. The image 106 is presented on a directive projection screen108, which is shown mounted on a wall of the room. The directiveprojection screen 108 may be located in other places, and it may beimplemented as a portable screen that can be set up at essentially anylocation within the room.

A line of viewing 110 extends from the image 106 to a viewer 112, who isshown standing in the room. The line of viewing 110 is shown assubstantially horizontal as the viewer 112 is standing up. In otherarrangements, the line of viewing 110 may be angled relative to thefloor as the viewer 112 may be sitting in a recliner, or the screen 108may be positioned lower on the wall below the viewer's eye level.

The room may include several non-projector light sources, such as awindow 114, an overhead light fixture 116(1), a table lamp light fixture116(2), and so forth. These non-projector light sources may produceinterfering light 118 that impinges upon at least a portion of thedirective projection screen 108. This interfering light 118 may degradethe image 106 to the point that the presentation to the viewer 112 isunacceptable.

There may be more than one directive projection screen in the room. Inaddition to the wall mounted screen 108, other wall mounted screens maybe positioned about the room, or surfaces (such as a table surface) maybe employed to reflect a projected image. In some implementations, aportable directive projection screen 120 may also or alternatively beused. The portable directive projection screen 120 is shown resting onthe table, but may be carried by the viewer 112 or otherwise movedeasily around the room. The problem of image degradation due to externallights is worse for the portable directive projection screen 120, giventhat variations in angle and position of the screen relative tointerfering light sources may change during use.

The projector 102 may be configured to track the portable screen 120during movement within the room and project an image onto it forpresentation. For example, text for an electronic book may be projectedonto the portable directive projection screen 120 for reading by theviewer 112. Tracking may be accomplished by recognizing the shape of thescreen 120, following optical targets disposed on the screen, and soforth.

The various directive projection screens 108 and 120 are designed toreflect incoming light in a directed manner. The screens 108 and 120include features that can be oriented and arranged to reflect aprojected image in one direction while reflecting interfering light inanother, or to project the image in two directions to produce a 3Deffect, or both.

In one implementation, the directive projection screens may comprise astructural substrate such as a foam core, plastic sheet, and so forth.The longest linear dimension of the substrate, when in use, isapproximately 60 centimeters or less. The weight of the portabledirective projection screen 120 may be less than three kilograms in someimplementations. The structural substrate may be configured to be rigid,foldable, rollable, and so forth. Atop the structure substrate is asheet of material that is embossed with features that directionallyreflect the projected images. The features are oriented in analternating pattern, allowing the passive screen to reflect a projectedimage to present a left eye image to the left eye and a right eye imageto the right eye. That is, the projected image is directed from thisembossed layer of the screen in two directions: a left side direction122 oriented to one side of the line of viewing 110 for the viewer'sleft eye to see, and a right side direction 124 oriented to the otherside of the line of viewing 110 for the viewer's right eye to see. Thisyields a 3D experience for the viewer.

As noted above, the projector 102 is implemented as part of an augmentedreality functional node 126, which includes one or more cameras 128 tocapture images of the room. In some situations, two camera(s) 128 may beused to track the projected image from the screen 108 or portable screen120 to determine which pixels of the projected image appear in the leftimage features and which pixels of the projected image appear in theright image features. The left image features reflected along direction122 would be visible by the viewer's left eye and the right imagefeatures reflected along direction 124 would be visible by the viewer'sright eye. The node 126 maintains a map of left and right eye pixels todisplay the left and right image components for the viewer to see a 3Dimage.

The node 126 may also be used to create an augmented realityenvironment. In this situation, the projector 102 may be used to projectstructured light patterns onto the surroundings of the room and thecamera 128 captures the images. The structured light patterns may useinvisible light so that the human viewer 112 does not detect thepatterns.

Example Implementations of Directive Projection Screen

FIG. 2 illustrates a first configuration 200 of the directive projectionscreen in which the screen returns images to the viewer 112 whilerejecting the interfering light. In this illustration, the portabledirective projection screen 120 is shown, although mounted screen 108may be similarly configured.

A normal 202 is shown perpendicular or orthogonal to a plane of thedirective projection screen 120. An acceptance cone 204 is shown whichdescribes an angle relative to the normal 202. The acceptance cone 204is the angular range within which incident light 206 will be acceptedand reflected generally back towards the viewer 112. For example, asshown here, the light 206 from the projector 102 is within theacceptance cone 204 and is thus reflected back to the viewer 112. Insome implementations, the acceptance cone 204 may extend 30 degrees fromthe normal 202. Incident light which is outside the acceptance cone 204is rejected. For example, incident light 208 from the light fixtures116(1) and 116(2) impacts the screen 120 outside of the acceptance cone204 (i.e., greater than 30 degrees from the normal 202). The screen 120is configured to reject this otherwise interfering light. This rejectionmay comprise redirection of the light away from the viewer 112,absorption of the light, and so forth.

A viewing cone may describe an angular range in which the viewer 112 isable to view the image 106. In the example above, the acceptance cone204 and the viewing cone may be coincident.

FIG. 3 illustrates an enlarged portion 300 of the directive projectionscreen 120 (or 108). A top view 302 is taken looking down on the screen120, and magnified to show a plurality of optical elements 304(1),304(2), . . . , 304(O). The optical elements 304(1)-(O) may be arrangedin a number of ways. In this illustration, the elements are arranged ina matrix of linear rows and columns. The optical elements 304 compriseoptical waveguides that conduct light. The optical elements 304 mayinclude, but are not limited to, optical fibers as shown here.

Each optical fiber of an element 304 comprises a core 306 surrounded bya thin cladding 308. The core 306 may be formed of a light conductingmaterial, such as glass, plastic, crystalline material, and so forth.When the optical elements 304 comprise optical fibers, the refractiveindex of the core 306 may be about 1.589 while the refractive index ofthe cladding 308 is about 1.517.

The optical elements 304(1)-(O) may be sized such that their width ordiameter is equal to or less than a minimum width of a projected pixel.In the example shown here, an inner diameter 310 of the core 306 may beabout 94 microns, while an outer diameter 312 of the surroundingcladding 308 may be about 100 microns. Accordingly, individual opticalelements 304(1)-(O) are about 100 microns, although they may be smaller.

The optical elements 304 may be held in place or distributed within amatrix configured as an optical absorber 314. The optical absorber 314is configured to be highly absorptive of visible light frequencies. Forexample, the optical absorber 314 may comprise black glass, carbonblack, or a dark pigment. The matrix may aid in maintaining the opticalelements in a generally parallel arrangement with one another.

Behind the optical elements 304 is a back reflector 316. This backreflector 316 is optically coupled to the optical elements 304, and isconfigured to be highly reflective to visible light frequencies. Forexample, in some implementations the back reflector 316 may comprise asputtered aluminum mirror. The reflector may be configured to act as anotch filter, reflecting light of particular frequencies. In someimplementations, different back reflectors 316 may be configured to actas different optical notch filters for different optical elements 304.These optical notch filters may include a fiber Bragg grating configuredto reflect a particular wavelength of light, a plurality of opticalinterference films having different refractive indices, and so forth.

Each optical element 304 is elongated, projecting outward from the backreflector 316. FIG. 3 illustrates a side view 318 of one optical element304. Light enters the optical element 304 via an input deflector 320disposed at the entrance or front of the optical element 304. The inputdeflector 320 is configured to alter a direction of incident light, andprevents an input angle from matching an exit angle. Such alterationexpands the viewing cone and improves the angular range relative to thenormal 202 within which the viewer 112 may see the image 106. As shownhere, the input deflector 320 may comprise a concave feature present inthe optical element 304. For example, an optical fiber may be ground oretched to produce the described concavity. The radius of curvature ofthe concavity of the input deflector 320 may vary. In the implementationshown, the radius of curvature is about 167 microns. In someimplementations, the input deflector 320 may comprise a plano-concavelens optically coupled to the front of the optical element 304. Inanother implementation, a plurality of optically refractive elements maybe used, such as glass or plastic beads.

As shown here, incoming light 321 incident on the optical element 304within the acceptance cone 204 enters the input deflector 320 andundergoes a change in direction. The light continues down the opticalelement 304 by internal reflection, reaches the back reflector 316, andis reflected the back down the optical element 304 for eventual exit asreflected light 206. In contrast, incoming light 208 incident on theoptical element 304 at an angle outside of the acceptance cone 204enters the input deflector 320, but fails to transfer down the opticalelement 304 via internal reflection. Instead, the light is readilyabsorbed by the optical absorber 314 and hence rejected in that it isnot reflected out from the optical element 304.

The optical element 304 has a length 322 from front to the backreflector 316. In one implementation, the length 322 may be a multipleof about five to ten times the outer diameter 312. In anotherimplementation, the length 322 may be at least ten times the outerdiameter 312. The optical element length 322 may vary between opticalelements 304 within the screen.

FIG. 4 illustrates an enlarged portion 400 of the directive projectionscreen 120 (or 108), which comprises an array of tapered optical guides.A top view 402 taken from the screen 120 and magnified shows a pluralityof optical elements 404(1), 404(2), . . . , 404(O). The optical elements404(1)-(O) are arranged linearly in columns, with a half width offset sothat the hexagonal perimeters nest with one another as shown. Inaddition to the top view 402 of the optical elements, a side view 405 isalso illustrated.

Each of the optical elements 404(1)-(O) have a varying contour thatincludes an upper hexagonal taper 406, a middle cylindrical taper 408,and lower a compound parabolic concentrator 410. At the base of eachoptical element is a convex reflector 412. While an initial taper of ahexagon is shown, in other implementations one or more other shapes maybe used. An outer diameter 414 of the optical element is tailored to anexpected size of the projected pixels comprising the image 106. Forexample, the width or outer diameter 414 may be about 100 microns. Areflector diameter 416 may vary according to the arrangement of thecompound parabolic concentrator 410. In one implementation, thereflector diameter 416 may be about 36 microns in diameter and have aradius of curvature of about 170 microns. As above, the convex reflector412 may comprise sputtered aluminum. The reflector may be configured toact as a notch filter which reflects light of particular frequencies. Insome implementations, the different reflectors may be configured withdifferent optical notch filters.

Disposed behind the optical elements 404 is an optical absorber 418. Theoptical absorber 418 is configured to be highly absorptive of visiblelight frequencies. For example, the optical absorber 418 may comprisecarbon black, or a dark pigment.

As shown in the side view 405, the optical elements 404 are disposedgenerally in parallel with one another, and perpendicular to a plane ofthe screen 120 in which they reside. The optical elements 404 comprisean optically transparent material 422. For example, in someimplementations, a clear flexible silicone elastomer may be used. Inother implementations acrylic, other polymers or glass may be used.Between portions of the optical elements 404 is an interstitial space,which may be filled with an interstitial material 424 such as anaerogel, gas, plastic, and so forth. A substantially planar front face426 is shown at the front of the optical elements 404. The opticalelements 404 may be individual elements and discrete from one another,or form sections or groups, such as shown here where the same opticallytransparent material 422 forms at least four of the optical elements 404and the front face 426.

The side view 405 shows the transition from the front face 426 havingthe hexagonal taper 406 with a hexagonal cross section, then to thecylindrical taper 408 having a cylindrical cross section and finally tothe compound parabolic concentrator 410 having a cylindrical crosssection. Stated another way, from the front face 426, the opticalelement 404 transitions from a hexagonal prism in the hexagonal taper406 to a cylinder in the cylindrical taper 408 to the compound parabolicconcentrator 410. Within a focal point at a base of the compoundparabolic concentrator 410 is the convex reflector 412. The convexreflector 412 is disposed such that the convexity extends towards thefront face 426.

As shown here, reflected light 206 is light which is incident within theacceptance cone, enters the front face 426 and proceeds through theoptically transparent material 422 via internal reflection. The light isconcentrated via the compound parabolic concentrator 410 onto the convexreflector 412, where the light is reflected back out through the opticalelement 404. The reflected light 206 leaves the optical element 404 at adifferent angle compared to an entry angle. As mentioned above, thisimproves viewability by expanding the viewing cone within which theviewer 112 is able to see the image 106.

In contrast, rejected light 208 enters at an incident angle outside theacceptance cone and eventually exits the optically transparent material422 through the interstitial material 424, where it is absorbed by theoptical absorber 418. As a result, light outside of the acceptance coneis effectively rejected, improving the presentation of light from theprojector 102 which is within the acceptance cone.

In another implementation, the front face 426 may comprise a separatesheet coupled to the optical elements 404 at or near the front edge ofthe hexagonal taper 406. Each optical element 404 has an optical elementlength 428 that extends from an outermost edge of the front face 426 tothe optical absorber 418 may be between 200 and 500 microns. Omittingthe front face 426, a linear distance from the front of the hexagonaltaper 406 to the optical absorber 418 may be about 300 microns.

In some implementations, when the optically transparent material 422 isdeformable, the convex reflector 412 may be a surface feature of theoptical absorber 418. Upon assembly, the convex reflector 412 maycompress at least a portion of a tip of the optically transparentmaterial 422. For example, in one implementation the optical absorber418 may comprise black acrylic having convex reflector surface features.When assembled with the optical elements 404 comprising flexiblesilicone, the convex reflector surface features compress the flexiblesilicone of the optical elements 404. This results in the placement ofthe convex reflector 412 within the compound parabolic concentrator 410of the optically transparent material 422.

FIG. 5 illustrates an enlarged portion 500 of a directive projectionscreen 120 (or 108), which includes an array of convex lenses havingfront surfaces and back surfaces with back mirrors. A top view 502 takenfrom the screen 120 and magnified shows a plurality of optical elements504(1), 504(2), . . . , 504(O) forming part of the projection screen.Each optical element 504 has a front surface or lens 506, a back surfaceor lens having about the same diameter, and a back reflector 508disposed on or proximate to the back lens. These lenses may bespherical, aspherical, or a combination thereof. As described above, theoptical element 504 may be sized such that its width or diameter isequal to or less than a minimum width of an estimated size of pixelsfrom the projector 102. In one implementation, the optical element 504has an outer diameter 510 of the front and back surfaces that is about100 microns. A reflector diameter 512 is also shown, which is less thanthe outer diameter 510 of the lenses.

A side view 514 depicts the composition of the optical elements 504. Theoptical element 504 is formed of an optically transparent material 516,such as a clear silicone material. This may be a single piece ofmaterial, or a plurality of pieces bonded together. An optical absorber518 is positioned behind the optical elements 504, and is configured tosubstantially absorb incident visible light.

The optical element 504 may be visualized as a convex back lens section520 and a convex front lens section 522. The back lens section 522comprises back surfaces which have a radius of curvature which isgreater than a radius of curvature of the front surfaces. For example,the radius of curvature of the front lens may be about 55 microns whilea radius of curvature of the back lens may be about 222 microns. Theselenses may be spherical or aspherical.

At least a portion of each of the back surfaces is configured with theback reflector 508. For example, as shown here, the back reflector 508is radially symmetrical about an optical axis and is configured with adiameter of about two-thirds the diameter of the back lens. In otherimplementations, the back reflector 508 may be displaced along the backof the back lens, asymmetrical, or both. Continuing the example abovewhere the outer diameter 510 is about 100 microns, the back reflector508 may be about 70 microns in diameter.

The optical absorber 518 is positioned behind the back lens section 520.As above, the optical absorber 518 is configured to be highly absorptiveof visible light frequencies. For example, the optical absorber 518 maycomprise carbon black or a dark pigment. In some implementations, theoptical absorber 518 and the back reflectors 508 may be incorporatedinto a single structure. For example, a black plastic sheet acting asthe optical absorber 518 may be coated with sputtered aluminum inparticular spots to form the back reflectors 508.

As shown here, reflected light 206 is initially directed incident withinthe acceptance cone, entering the optically transparent material 516,and then reflected back from the back reflector 508. In contrast, therejected light 208, which is received at an angle outside the acceptancecone enters the optically transparent material 516 and is directed intothe optical absorber 518.

FIG. 6 illustrates an enlarged portion 600 of a directive projectionscreen 120 (or 108), which includes a plano-convex lens array with anoptical absorber having apertures and a back mirror. As shown here in atop view 602, the screen 120 has a plurality of optical elements 604(1),604(2), . . . , 604(O). These optical elements 604(1)-(O) comprise alens array 606, an optical absorber 608, and a back reflector 610.Lenses in the lens array 606 may be spherical or aspherical andplano-convex in profile, having a convex side and a planar side. Theoptical absorber 608 is formed of a material to substantially absorbincident visible light frequencies, as described above. The backreflector 610 is configured to substantially reflect incident visiblelight frequencies. For example, the back reflector 610 may comprisealuminum. In some implementations, the optical absorber 608 and the backreflector 610 may be combined. For example, the optical absorber 608 maybe printed on the back reflector 610.

As shown here, a lens diameter 612 is shown, along with a correspondingaperture diameter 614 which is less than the lens diameter 612. In otherimplementations, the diameters may be about the same.

A side view 616 shows the lens array 606 comprising an opticallytransparent material 618 such as glass, plastic, and so forth. Behindthe lens array 606 is the optical absorber 608, which is formed withmultiple apertures 620. The apertures 620 may be substantially alignedwith the lenses, or offset to alter the acceptance cone, viewing cone,or both. As shown here, the reflected light 206 enters within theacceptance cone and is reflected by the back reflector 610. In contrast,the rejected light 208 is diverted into the optical absorber 608.

The lens array 606 has a thickness 622, which may vary based on thematerial employed. When the optically transparent material 618 of thelens array 606 comprises plastic, the thickness 622 of the lens array606 may be about 1.5 times a radius of curvature of the plano-convexlenses. In another implementation, the thickness 622 of the lens arraymay be equal to or less than one-half of a lens focal length.

Example Implementations of Passive Projection Screen for 3D

FIG. 7 illustrates another configuration 700 of the directive projectionscreen in which the screen returns projected images to the viewer 112 ina way that appears three dimensional (3D) to the viewer. In thisillustration, the mounted directive projection screen 108 is shown,although the portable screen 120 may be similarly configured. Aprojector 102 projects light onto the passive screen 102, where it isscattered and reflected back as an image to the viewer 112.

Generally, the projection screen 108 has an array of optical elementsthat allows the viewer 112 to see one portion of the projected imagewith his left eye 702 and another portion of the projected image withhis right eye 704. More particularly, the incident light 706 projectedfrom the projector 102 onto the screen 108 is received by the opticalelements of the screen 108. The image has pixel sizes that are smallerthan the size of the individual optical elements. The optical elementsreflect part of the image in a direction 708 toward the viewer's lefteye 702 and part of the image in another direction 710 toward theviewer's right eye 704. The angular difference of the reflected lightforms a parallax effect for the human viewer. In this manner, the viewerperceives the reflected image as 3D, thereby facilitating a 3Dexperience without the viewer needing to where special 3D glasses.

There are several ways to implement this 3D effect using a passivescreen. Three different techniques are described below with reference tothe implementations of FIGS. 8-10. In these implementations, the opticalelements share a common characteristic in that, pixel by pixel, asurface feature of the screen enables the viewer's left eye to see oneimage and the viewer's right eye to see a different image.

FIG. 8 shows a first implementation 800 of a passive display screen forpresenting projected images in 3D. In this view, the directiveprojection screen 108 (or 120) has an array of optical elements formedon one surface used to present an image projected by projector 102. Amagnified view of one optical element 802 is shown expanded from thescreen 108. The optical element 802 is formed as an elongated body 804that defines a hollow well or cavity 806 therein. The body 804 may beformed as a cylindrical tube having a circular cross-section. As oneexample implementation, the cylindrical tube has a diameter equal to orless than about 100 microns. Alternatively, the body 804 may be formedas other structure members with other cross-sectional shapes, such asoval or polygonal.

The body 804 may be formed of any suitable material, such as plastic.The internal surface of the body 804 may also be reflective to conveythe light rays down through the cavity 806 to the base of the body 804.

At the base of the body 804 is a reflector 808 that reflects lightreceived through the cavity 806 from the projector 102. The reflector808 may be formed of any type of reflection material, such as thosementioned above in earlier implementations. The reflector 808 may have aperimeter shaped to correspond with the shape of the interior surface ofthe body 804. Hence, if the body 804 is a cylinder with a circularcross-section, the reflector 808 may also have a circular perimeter asillustrated in FIG. 8. However, the reflector's perimeter may be formedin shapes other than circular. Additionally, the reflector 808 may alsobe formed with a reflection surface that is flat, concave, or convex. Aflat surface is shown as reflector implementation 808A in FIG. 8.Additionally, the reflector 808 may have a continuous reflectionsurface, such as reflector 808A, or exhibit a discontinuity, such as twoflat regions being joined at an angel, as shown in reflectorimplementation 808B.

The body 804 of optical element 802 has a length L from a first, inner,or base end 810 adjacent the reflector 808 to a second, outer, or topend 812 that is distal to the reflector. The length L of the body 804,the position of the projector 102, and the focus of the image projectorthereon are coordinated to provide a parallax effect for the humanviewer. This parallax effect allows the human's left eye 702 to see partof the image being reflected from the reflector 808 and the human'sright eye 704 to see another part of the reflected image. This isillustrated in FIG. 8.

Suppose, for example, the projected image containing multiple pixels isdirected into the well 806 formed by the body 804. The image isreflected by the reflector 808. Due to the elongated shape of the body,the well 806 is sufficiently deep that the viewer's right eye 704 seesonly a portion of the image, such as the left half side of thereflector. This is represented by the “R” in the left half side of thecircular reflector representation 814. Similarly, the viewer's left eye702 sees only a portion of the image, such as the right half side of thereflector, as represented by the “L” in the right half side of thecircular reflector representation 814.

The projector 102 may project dual portions of the image onto the screen108, in which a first image is projected into and reflected from theleft half of the well 806 and reflector 808, and a different secondimage is projected into and reflected from the right half of the well806 and reflector 808. In this manner, the right eye sees a differentimage than the left eye, enabling a 3D experience.

When the projector 102 and the screen 108 are both fixed, the challengeof projecting two different images onto the different portions of theoptical elements 802 can be controlled. However, for a mobile surface,such as the portable screen 120, the problem of projecting the dualimage onto the surface is more difficult. In this situation, theprojector employs a tracking mechanism that observes the images beingprojected onto the surface and attempts to track movement of the screen,and adjust the projection direction accordingly. As one implementation,the projector 102 may be part of a node 126 having a camera 128 forcapturing the images projected onto the surface of a screen (such asscreen 120). As the screen is moved, the camera 128 senses the movementand observes the reflected images. This information is fed back to acomputing unit at the node 126 (or remote therefrom) that computes a newprojection angle and focus, and provides these new parameters to theprojector 102.

In this manner, the projection system is able to track the image on thescreen to determine which pixels of the projected image appear in oneportion of the wells 806 of the elements 802 and would be visible by theleft eye 702 and which pixels appear in another portion of the wells 806of the elements 802 and would be visible by the right eye 704. This mapof left and right eye pixels may be maintained by the computing unit todisplay the left and right image components for the viewer to see a 3Dimage.

FIG. 9 shows a second implementation 900 of a passive display screen forpresenting projected images in 3D. In this view, the directiveprojection screen 108 (or 120) has an array of optical elements formedon one surface used to present an image projected by projector 102. Fordiscussion purposes, the optical elements may be configured as element802 shown in FIG. 8. One of the challenges noted above, is attempting totrack the left and right side images, particularly when the projectionscreen is being moved. In implementation 900, the tracking function issignificantly reduced or even eliminated through use of polarizationlenses placed at the opening of the bodies 804.

A top and magnified view 902 of the screen 108 is illustrated to show aplurality of optical elements 904(1), 904(2), . . . , 904(O). Theoptical elements 904(1)-(O) may be arranged in a number of ways. In thisillustration, the elements are arranged in a matrix of linear rows andcolumns. Each optical element 904 has a body 804 (see FIG. 8) overlaidwith an associated polarizer 906. A polarizer is an optical filter thatpasses light of a specific polarization. It may also block light ofother polarizations. Two common types of polarizers are linearpolarizers and circular polarizers.

As illustrated, the polarizers 906(1)-(O) have two polarizationpatterns: horizontal and vertical. As one example, alternating opticalelements are fitted with horizontal polarizers 908, and the remainingoptical elements are fitted with vertical polarizers 910. This forms acheckerboard pattern of alternating polarizers overlaid on the wells inthe optical elements. Other patterns may be used, such as alternatingrows or alternating columns, for small contiguous groups of elementshaving differing polarizations, and so forth.

The projector 102 generates a corresponding polarized light fortransmission to the screen and polarizers 906(1)-(O). For instance, theprojector 102 may employ a color wheel with one set of segmentspolarized a first direction and a second set of segments polarized asecond direction. In this manner, the light projected through the firstset of segments is received and passed by the horizontal polarizers 908and the light projected through the second set of segments is receivedand passed by the vertical polarizers 910. One advantage of using acolor wheel with two sets of segments is that the projected image mayexhibit increased brightness when used on a surface or screen that doesnot have the polarizers 906.

With this arrangement, the projector 102 generates a left eye imageusing one polarization and a right eye image using a secondpolarization. As illustrated, the left eye 702 may perceive the imagepassed by the vertical polarizers 910 while the right eye 704 mayperceive the image passed by the horizontal polarizers 908.

FIG. 10 shows a third implementation 1000 of a passive display screenfor presenting projected images in 3D. In this implementation, twoprojectors 102A and 102B are used to project an image onto the directiveprojection screen 108 (or 120). The screen 108 has an array of opticalelements that are configured in a way to present acceptance cones ofincident light. Accordingly, the optical elements may be configured asshown and described, for example, as the elements 304 in FIG. 3,elements 404 in FIG. 4, elements 504 in FIG. 5, and elements 604 in FIG.6.

However, unlike the optical element patterns shown in these earlierconfigurations, the elements are arranged to present different angledacceptance cones, as represented by a first acceptance cone 1002 and asecond acceptance cone 1004. The cones are oriented to accept light fromone projector while rejecting light from the other. More particularly,the first acceptance cone 1002 accepts the projected light 1006 from theprojector 102A, while rejecting the light 1008 from the projector 102B.Similarly, the second acceptance cone 1004 accepts the projected light1008 from the projector 102B, while rejecting the light 1006 from theprojector 102A. The angled acceptance cones, relative to the surfaceplane of screen 108, may be accomplished by angling the optical elementsrelative to the screen substrate. Thus, first elements may be arrangedor angled relative to the screen substrate to provide the firstacceptance cone 1002 and second elements may be arranged or angledrelative to the screen substrate to provide the second acceptance cone1004. The optical elements may be angled in an alternating, checkerboardpattern, or arranged such that every other row or column has the sameangle, or in any other suitable groupings.

The two projectors 102A and 102B project different images to provide aleft image and a right image. The left image is accepted by all of theleft leaning acceptance cones 1002 and the right image is accepted byall of the right leaning acceptance cones 1004. The human viewer 112sees, in left eye 702, the left image accepted by the first acceptancecone 1002 and reflected back to the viewer. The human viewer 112 alsosees, in right eye 704, the right image accepted by the secondacceptance cone 1004 and reflected back to the viewer.

Polarizers may optionally be added to the optical elements as describedabove.

FIG. 11 shows a fourth implementation 1100 of a passive display screenfor presenting projected images in 3D. In this implementation, aprojector 102 projects an image onto the directive projection screen 108(or 120) from an angle, such as from the side or from overhead. A viewer112 is shown watching the screen 108 from a position approximatelynormal to the screen surface. A left eye 702 and a right eye 704 of theviewer 112 are represented.

The screen 108 is formed of several passive layers or elements. A topedge view 1102 of the screen is enlarged to show these layers. Thescreen 108 includes a back layer 1104 formed of a material to scatterlight projected thereon by the projector 102. The back layer 1104 may berigid or flexible. The surface may be white or other color, with acontour sufficient to scatter light.

A polarization layer 1106 overlays the back layer 1104. The polarizationlayer 1106 is composed of a pattern of areas, where each area has atleast one type of polarization. In one implementation, the polarizationareas is an array of alternating polarizer strips, including firstpolarizer strips 1108 having a first polarization and second polarizerstrips 1110 having a second polarization. The first polarizer strips1108 pass light having first image components of the first polarizationand the second polarizer strips 1110 pass light having second imagecomponents of the second polarization. The light is passed through thepolarization layer 1106 to the back layer 1104, where the light isscattered and depolarized

FIG. 12 shows one example pattern 1200 of the first and secondpolarizers of the polarization layer 1106. In this implementation, thefirst and second polarizers are interleaved to provide an alternatingpattern of first and second polarizations. As one example, the firstpolarizer strips 1108 are formed with a clockwise polarization, whilethe second polarizer strips 1110 are formed with a counterclockwisepolarization. In another example, the first polarizer strips 1108 areformed with vertical polarization, while the second polarizer strips1110 are formed with horizontal polarization. Each of the polarizerstrips 1108 and 1110 has a small width, with an example width beingapproximately one pixel (e.g., 50 to 300 microns).

With reference again to FIG. 11, the screen 108 further includes aparallax barrier layer 1112 with a parallax barrier oriented along anangle of the expected projection. As shown, the parallax barrier isformed of spaced opaque slats or regions 1114. The opaque regions 1114may be angled or otherwise have a dimensional aspect that allows theparallax barrier to receive the light from the projector 102 without anysubstantial blocking. Light 1116 emitted from the projector 102 passesthrough gaps between the opaque regions 1114, allowing most all of thelight to reach the polarizing filters. Also, in the illustratedimplementation, the opaque regions 1114 may be arranged adjacent to onetype of polarization strips (e.g., second polarizer strips 1110), whilethe gaps are adjacent to the other type of polarization strips (e.g.,first polarizer strips 1108).

A transparent layer 1118 is also provided to hold the parallax barrierlayer 1112 in a spaced distance from the polarization layer 1106. Thetransparent layer 1118 also provides a protective surface of the screen,while passing light therethrough. The transparent layer 1118 may beformed of any type of light transmissive material, such as plastic,acrylic, or COC.

In operation, light 1116 is projected from the projector 102 with twotypes of polarization. Each polarization has one of the views or imagesthat make up a 3D binocular view. The opposite polarization types arecombined into a single beam of light and emitted from the projector. Thecombined polarization types (e.g., vertical and horizontal) arerepresented pictorially by a symbol 1118 formed of a circle with a linetherethrough. The light 1116 approaches the screen 108 at an angle, suchas over the viewer's shoulder or off to one side. The light 1116 passesthrough the transparent layer 1118, through the opaque regions 1114 ofthe parallax barrier layer 1112, and onto the polarization layer 1106.The polarization strips 1108 and 1110 only permit light of oneparticular type of polarization while rejecting or quenching the other.For instance, the first polarization strips 1108 may pass light of afirst polarization (e.g., vertical or clockwise) while rejecting lightof a second polarization (e.g., horizontal or counterclockwise).Concurrently, the second polarizing strips 1110 would pass light of thesecond polarization (e.g., horizontal or counterclockwise) whilerejecting light of the first polarization (e.g., vertical or clockwise).The light that is passed by the polarization layer 1106 hits the surfaceof the back layer 1104 and is scattered. The light is also depolarized.The left and right images are interleaved, so that pixel-wide strips ofthe left image alternate with pixel-wide strips of the right image.

The light is scattered back toward the human viewer 112. The parallaxbarrier layer 1112 blocks and passes light to respective left eye 702and right eye 704 along first and second lines of sight. For instance,light passed by the first polarizer strips 1108 may be visible throughthe parallax barrier to the left eye 702 along a first line of sight,while blocking the path to the right eye 704. Similarly, light passed bysecond polarizer strips 1110 may be visible through the parallax barrierto the right eye 704 along a second line of sight, while blocking thepath to the left eye 702. This helps create a three-dimension visualeffect.

FIG. 13 illustrates a user scenario 1300 in which a viewer 1302 isholding a two-sided portable passive projection screen 1304. The vieweris shown sitting in a chair 1306, although the user may also be mobile,such as walking around a room or down a hall. The viewer 1302 is lookingat the first side or surface 1308 of the screen 1304. The first side1308 facilitates viewing of images projected by the projector 102 in twodimensions. The first side 1308 may be formed using a traditionalreflective surface or alternatively, as a directive projection screensuch as any one of the implementations described above with respect toFIGS. 3-6.

The viewer 1302 may alternatively flip the screen 1304 so that a secondside or surface 1310 is exposed to the projector 102. The second side1310 facilitates viewing of images projected by the projector 102 in 3D.The second side 1310 may be formed according to any one of theimplementations described above with respect to FIGS. 8-12. Upondetecting the second side 1310 of the screen 1304, the projector 102begins projecting the right and left images to yield a 3D effect whenpresented on the screen. The camera 128 or other sensor on node 126 maybe used to distinguish between the first and second sides of the screen1304. In one implementation, for example, the second surface 1310 mayhave a registration mark 1312 depicted thereon to ensure easy detectionby the node 126.

Accordingly, the portable projection screen 1304 may be used to viewimages either in 2D or 3D, simply by flipping the screen to expose adifferent surface of passive optical elements. The different surfacesmay allow for viewing conditions that are suitable for different typesof content. For instance, text content like books may be projected ontothe 2D surface 1308, whereas videos may be projected onto the 3D surface1310.

CONCLUSION

Although the subject matter has been described in language specific tostructural features, it is to be understood that the subject matterdefined in the appended claims is not necessarily limited to thespecific features described. Rather, the specific features are disclosedas illustrative forms of implementing the claims.

What is claimed is:
 1. A device, comprising: a back layer configured toreceive light from a projector on a front side of the device and toscatter the light back from the front side of the device, the lightreceived from the projector having first image components of a firstpolarization and second image components of a second polarization; apolarization layer adjacent the back layer, the polarization layerhaving at least first and second polarization areas, the firstpolarization areas substantially passing the light having the firstimage components of the first polarization and the second polarizationareas substantially passing the light having the second image componentsof the second polarization; and a parallax barrier layer adjacent to,but spaced from, the polarization layer, the parallax barrier layerforming a parallax barrier so that the first image components returnedby the back layer are viewable through the parallax barrier along afirst direction and the second image components returned by the backlayer are viewable through the parallax barrier along a seconddirection.
 2. The device of claim 1, wherein the first polarization isvertical and the second polarization is horizontal.
 3. The device ofclaim 1, wherein the first polarization is clockwise and the secondpolarization is counterclockwise.
 4. The device of claim 1, wherein thefirst and second polarization areas are formed as elongated strips. 5.The device of claim 1, wherein the first and second polarization areasare formed as elongated strips, such that first strips of the firstpolarization are interleaved with second strips of the secondpolarization.
 6. The device of claim 5, wherein the parallax barrierlayer has opaque regions spaced apart from one another to form gapsbetween adjacent opaque regions, the opaque regions being arranged tooverlay one of the first strips or the second strips, while the gapsoverlay the other of the first strips or the second strips.
 7. Thedevice of claim 6, wherein the opaque regions are angled to pass thelight from the projector when projected at an angle to the projectionscreen.
 8. The device of claim 1, wherein the parallax barrier layer hasopaque regions.
 9. A projection system comprising: a passive displayscreen comprising: a back layer configured to receive light from aprojector on a front side of the device and to scatter the light backfrom the front side of the device, the light received from the projectorhaving first image components of a first polarization and second imagecomponents of a second polarization; a polarization layer adjacent theback layer, the polarization layer having at least first and secondpolarization areas, the first polarization areas substantially passingthe light having the first image components of the first polarizationand the second polarization areas substantially passing the light havingthe second image components of the second polarization; and a parallaxbarrier layer adjacent to, but spaced from, the polarization layer, theparallax barrier layer forming a parallax barrier so that the firstimage components returned by the back layer are viewable through theparallax barrier along a first direction and the second image componentsreturned by the back layer are viewable through the parallax barrieralong a second direction; and a projector to project the light onto thepassive display screen.
 10. The projection system of claim 9, whereinthe first and second polarization areas are formed as elongated strips,such that first strips of the first polarization are interleaved withsecond strips of the second polarization.
 11. The projection system ofclaim 10, wherein the parallax barrier layer has opaque regions spacedapart from one another to form gaps between adjacent opaque regions, theopaque regions being arranged to overlay one of the first strips or thesecond strips, while the gaps overlay the other of the first strips orthe second strips.
 12. The projection system of claim 11, wherein theopaque regions are angled to pass the light from the projector whenprojected at an angle to the projection screen.
 13. The projectionsystem of claim 9, wherein the first polarization is vertical and thesecond polarization is horizontal.
 14. The projection system of claim 9,wherein the first polarization is clockwise and the second polarizationis counterclockwise.
 15. A device, comprising: a back layer configuredto receive light from a projector on a front side of the device and toscatter the light back from the front side of the device, the lightbeing received having first image components of a first polarization andsecond image components of a second polarization; a polarization layeradjacent the back layer, the polarization layer having firstpolarization strips interleaved with second polarization strips to passrespectively, to the back layer, the first image components of the firstpolarization and the second image components of the second polarization;and a parallax barrier layer adjacent to, but spaced from, thepolarization layer, the parallax barrier layer having a plurality ofopaque regions spaced apart from one another to form gaps betweenadjacent opaque regions, the opaque regions being arranged to overlayone of the first polarization strips or the second polarization stripswhile the gaps are arranged to overlay the other of the firstpolarization strips or the second polarization strips.
 16. The device ofclaim 15, wherein the first polarization is vertical and the secondpolarization is horizontal.
 17. The device of claim 15, wherein thefirst polarization is clockwise and the second polarization iscounterclockwise.
 18. The device of claim 15, wherein the first andsecond polarization strips are formed as elongated strips.
 19. Thedevice of claim 15, wherein the opaque regions are angled to pass thelight from the projector when projected at an angle to the device. 20.The device of claim 15, further comprising a substrate, wherein the backlayer, the polarization layer, and the parallax barrier layer arearranged on a first side of the substrate, and a second surface isprovided on an opposing second side of the substrate to present an imagein two dimensions.